Question about Welbilt MR95TW Microwave Oven
My mirowave oven has a mechanical timer, it is very simple made and the problem is that it heats very slowly. Can the temperature be increased?
A diode is an electronic component that readily passes current in one direction only and blocks the flow of current in the opposing direction. If your microwave's diode has become defective, your microwave will not heat. Test the diode to determine if this is the cause of your problem. Replace it if it is defective.
Testing a diode
NOTE: Before you test your diode, make sure your microwave is unplugged, and that you discharge the microwave's capacitor.
Whether it is shorted or open, a defective diode will most likely show some sign of defect. Defective diodes will usually emit an electrical burning smell, signifying its defectiveness. Also, it may have split in two, or it may exhibit a burned crack, or possibly even a blistered spot.
A shorted diode is indicated by a loud humming noise from the high voltage transformer, and no heat produced when a cook cycle is initiated. Whereas little or no heat produced in your microwave, with an absence of a humming noise is indicative of an open diode. In either case, the diode has to be replaced.
With your microwave unplugged, and your capacitor discharged, use extreme caution to remove the lead that leads to the capacitor. You can leave the ground connection attached. The side of the diode that goes to the ground is usually marked with a dot, stripe, or arrow. Set your ohmmeter to R x 10,000 or higher. Touch the positive meter probe to the anode and the negative meter probe to the cathode to measure the resistance across the diode terminals. Remember that the cathode is on the side that goes to the ground, which is often marked by a dot, stripe, or an arrow.
A normal diode, that is a non-defective diode, will read anywhere from 50,000 to 200,000 ohms. Differences in microwave make and model account for this large range in resistance readings.
Reverse the meter probes and measure resistance while touching the positive probe to the cathode and the negative probe to the anode. Reversing the probes like this should result in a reading of infinity. Unless a bleeder resistor is present. The presence of a bleeder resistor would produce a reading of the value of the resistor.
High Voltage Capacitor
A capacitor is an electrical device which stores electricity. A defective capacitor may be why your microwave is not heating. The capacitor will have to be tested to determine if this is the cause of your problem. A defective capacitor will have to be replaced before your microwave will work again. Make sure you discharge the capacitor before you test it, though.
A defective magnetron is the third possible cause of why your microwave is not heating. Test your microwave's magnetron. Replace it if it is defective.
Testing a magnetron
NOTE: Before you test this component, make sure your microwave is unplugged, and that you have discharged the capacitor.
There are two tests to conduct in order to determine whether or not a magnetron has become defective. If you receive results other than what are detailed below, you will have to replace your microwave's magnetron. Each test is described for you here:
TEST 1: Locate your magnetron and label each of the wires attached to it so that you know which wires are to be replaced where. Set your ohmmeter to the lowest resistance scale. Take a resistance measurement between each of the magnetron terminals by touching each probe to one terminal each. Reverse the probes and take a second resistance measurement. Each measurement should read less than one ohm.
TEST 2: Set your ohmmeter to its highest resistance scale. Touch one of the meter's probes to a magnetron terminal. Touch the other probe to the metal magnetron housing. Take special caution to not touch the two probes together. This could result in an inaccurate reading. This test should produce a reading of infinity - indicating an open circuit.
If you cannot perform the above task yourself, ask a family or friend that has the ability to assist you or have a certified and experienced appliance repair technician examine and replace your magnetron. This task is much too dangerous for the average layman to perform on his own.
Read the tips on the below links on how to replace your microwave oven's diode and how to discharge the capacitor.
I hope the above is helpful.
Posted on Jan 05, 2012
Eliom, two things: small microwave units are limited in their capacity and no microwave unit can be modified in any way that is safe. second, microwaves slowly lose power as the tube degrades.
Posted on Dec 19, 2007
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Posted on Jan 02, 2017
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It sounds like the magnetron may have
either failed or is not being supplied with the extremely high
voltage required to run it.
SAFETY IS PARAMOUNT
This is a job for a professional but if
you are safety clued up, here's instruction.
Make sure the !!!!capacitor is discharged!!!!! before attempting any sort of repair.
Check the door interlock switches first then the high voltage diode with either an AVO model 8 or moving coil meter on high resistance range for short circuit, (DVM's won't show the fault!), the capacitor can fail and go short circuit, the feed fuse on the primary of the high voltage transformer and then finally, the magnetron is best checked by substitution.
Hope that helps.
simple safety test.
Place 1/2 litre of water in a glass container. Measure the temperature of the water.
Place in microwave and heat on full power for 1minute.
Measure the temperature after it has stood for 1minute.
If the temperature difference is more than 9 degrees Celcuis the magnetron is working and producing about 700Watts of heat.
If your microwave is labelled with 900 or 1000Watts. That is about right.
If the temperature is less then the magnetron is not working properly and may need replacing.
This a only a rough guide and any doubts you should consult an authorised service agent.
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